Kudzu, which is a leguminous plant, has been used as a raw material for food, a raw material of Chinese herbal medicines and the like for a long time. For example, the starch from kudzu has been used as a raw material of traditional Japanese confectionery. The root and flower of kudzu, which are respectively called pueraria root and pueraria flower, have been used as raw materials of Chinese herbal medicines for antipyretic, analgesic and spasmolytic effects, and improvement of symptoms such as sweating.
Among these, pueraria flower is known to contain various components, including flavonoids. In recent years, it has become clear that pueraria flower has an effect of improving hepatopathy, an effect of preventing a hangover, an effect of improving urinary nitrogen metabolism, and other effects, which are not provided by other leguminous plants (e.g., Japanese Patent No. 3454718, Japanese Patent Publication No. 08-032632, and Japanese Laid-Open Patent Publication No. 64-68318). However, pueraria flower do not appear to have been studied for its functions extensively, and a new use of pueraria flower is desired.